Python - absolute position of face
Multiply it with the object's world matrix.

loc_world_space = obj.matrix_world * loc_obj_space


where loc_obj_space is a 3d mathutils.Vector

There is an addon View3D-> Math Vis(Console) available to visualize vectors and matrices directly in the viewport.

I.e. paste the following lines to the interactive console

obj = bpy.context.active_object
lobj = [vertex.co for vertex in obj.data.vertices]
lworld = [obj.matrix_world * vector for vector in lobj]